"Pricing is US $1.05 each for the IR1150S/IR1150SPbF and US $1.38 each for the IR1150IS/IR1150ISPbF..."
"The One Cycle Control method used in the IR1150 controller does not have an analog multiplier, input voltage sensing, or fixed oscillator ramp, simplifying circuitry and reducing component count. Instead, IR's OCC uses a proprietary integrator with a reset circuit: The output of the error amplifier is integrated over each clock cycle to generate a variable- slope ramp. This variable ramp is compared with the error voltage and subtracted from the current sense signal to generate the PWM gate drive."
That level of pricing is only obtained with legacy parts produced at paid-for yester-year backwater fabs. Not that there's anything wrong with those parts or fab lines; we depend upon them for ICs, etc., for lots of jelly-bean electronics products, such as PC power supplies.
IRF has introduced the IR1150S control IC. It contains a proprietary "one cycle control" for CCM PFC with no line voltage sense required. Pretty neat! But, can't we also use it in any DC/DC CCM loop, be it forward, flyback or boost as a voltage feedforward control loop without actually looking at the input voltage. Even better, will this controller not cure the dreaded Harmonic Oscillation in peak current controlled CCM loops operated at >50% duty? OMG, I just wet my pants. What say you, you power supply gurus? Cheers, Harry
Well, what does it cost? That is what it boils down to in the end. RHP problems could be handled with regular chips, too. But even those were too expensive in some of my designs so it ended up being all discrete or logic chips.
Thanks for the information. That is better than I thought, certainly a good deal for large PFC circuits. Regular switchers, maybe not. I am still holding out for something like the LM3478 but around 30 cents.
Maybe that's why my designs contain legacy parts almost exclusively. Sometimes though I have the feeling that some mfgs want to front load the amortization, trying to squish out whatever the market gives in the first couple years. Not the IR1150S, that one seems fair in price.
Front loading can really hinder market entrance. I have looked at several opportunities to swing a design to uC (MSP430). No chance, the jelly bean concoctions beat it all the time. At least they need to come out with a real bare bones version. It is amazing how cheap discrete SMT designs are these days. And when, for example, a switcher or PFC can be designed with CMOS logic then it's done that way.
I like your "even....S.Cuk" So Terry, will this controller cure sub harmonic oscillation in CCM >50% duty?? What about using it's voltage feedforward ability in DC/DC loops?
Keyue Smedley has written dozens of papers on one-cycle control; Dragan Maksimovic wrote a really nice paper on an OCC boost converter about 10 years ago. I figured out how it works once, but carefully forgot most of it. Basically its a non-linear modulating ramp, whose non-linearity is carefully chosen to automagically achieve (in this case) UPF. Heck, I've even seen an OCC paper by Slobodan Cuk.
The problem with OCC is that it requires integrators that get reset every cycle. Thats not so bad, but (until now) you have had to DIY these integrators. I have never built one to prove it, but I expect that making a practical device work is a lot trickier than it appears from the papers I have read (none of which give any detail of the resettable integrators). I imagine that IR have done a nice job though.
Their PF isnt too good at low load, high line though, its about 0.828 for 30W = 10% rated load at 230V (cf 0.985 at 115V). Although they have made little or no effort at controlling them, emissions are not bad.
I suspect the PF could be improved with peak input voltage feed-forward of some description, but that might prove tricky as there is no access to the on-chip integrators.
Or follow the route of the new age "instant design":
Key your parameters into a web interface and click.
Wait.
Wait some more.
Upon the message "parameters are outside the scope of this web design program", "design cannot be completed with entered parameters" or something like that, rip sheet off anger management pad on office wall.
Crumple anger management sheet and throw into corner of office. For maximum relief, do so with gusto.
Roll your own design. Heck, maybe you don't even need any fancy controller chip.
Hey, if Dr Cuk writes papers on it, it probably works. Unlike much of the crap published in some professional comics :), which look something like this:
design a topology have way too many magnetic components, switches, diodes and capacitors than necessary. If possible, ensure > 3 semiconductors in power path at all times.
write the NLTV equations for the system.
run thru maths package and draw pretty pictures
spice circuit - ie enter graphically, then let spice numerically extract & solve much the same equations as (2), and draw some more pretty pictures
Compare and contrast the pretty pictures. If they are very similar, pat self on back and proudly announce "it works" (or in other words the analytic solution mathced the numeric one)
Add to list of published papers, lean back at desk and sigh contentedly. Outside, the real world rushes madly by.
I think in general it will do so, but you can perhaps design one that doesnt.
OCC is by definition a non-linear controller, so there is no need to "linearize" (read as: pretend it is something it is not) the system before designing the controller. Quite the opposite in fact.
You design a One-Cycle Controller by developing a non-linear time-varying mathematical description of the converter to be controlled. We do this anyway when designing a conventional linear controller.
After adopting a suitable pose and expression, stare long and hard at the mathematical description, and voila - the desired OCC control law comes leaping out at you.
This is basically a kind of feedback linearization controller (eg Applied Nonlinear Control, Slotine, pp207-271). The idea is to cancel the nonlinearities in a nonlinear system so that the closed-loop dynamics are in a linear form. Traditional LTI system theory can then be used to design the controller, and assuming there are no model uncertainties the controller behaves as predicted, for large as well as small signals.
[linearisation is actually "do a taylor/maclaurin series expansion and throw almost all of it away". Often the bits you discard are important, which is why linearised controllers dont necessarily work so well for say large signals]
A simple example of this concept is a boost PFC. When designing the voltage control loop, if you use square of the DC bus voltage and compare it with the square of the setpoint voltage (trivial in s/w) - in other words implement a DC bus energy controller - then analysis shows the closed loop behaviour is in fact linear (assuming the current controller is fast enough to reach setpoint faster than the voltage loop sample time).
Its interesting that one method of nonlinear stability analysis, Lyapunovs 1st (or is it 2nd? someone will correct me im sure) method uses suitable "lyapunov functions" to check asymptotic stability. Common functions are the so-called "energy functions" that mathematically are similar to physics equations for energy like 0.5CV^2 etc. Oops, rambling...its because of the 2nd law of thermodynamics, real systems are always asymptotically stable (if not they would be perpetual motion or free energy machines) blurble.
that control systems label isnt necessarily right either - I suspect some OCC designs may look more like a straight nonlinear controller rather than the aforementioned feedback linearisation. who cares, its only a label, but the techniques are interesting.
A significant drawback with non-linear control is the lack of a handle-cranking mechanism for, say, proving stability, or even choosing a controller. Its a big nasty world out there....time to go shelter behing whats left of Maclaurin....
as usual, *it depends*. Each OCC strategy is (or can be) unique - define your system, design the controller. A literature search will save you a fair chunk of work here, but in practice if you're gonna design a loop you might as well analyse the entire thing. Or at least load up the last mathcad file, save as and twiddle the numbers....
One potential problem with feedback linearisation is its robustness to parameter variations. Some implementations may be very sensitive, others may not. The published results I've read for many OCC converters look pretty good, probably because the integration smooths over any errors. But I betcha you could come up with really lousy OCC's if you tried :)
I (hopefully) have a project coming up where I will implement a whole raft of feedback linearisation controllers. Maybe they will even work.....the idea is to implement non-linear controllers to enable the system to maintain control (not saturate) for large setpoint & load changes, along with a high closed-loop bandwidth for relatively low sampling rates. This stuff (in some respects) is quite easy in a DSP, whereas a lot of it is a pig in hardware (until IR, ST etc. make nice cheap chips)
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